Most optical communication systems use optical fibers to propagate optical data signals because optical fibers have very low optical attenuation, wide bandwidths, and are secure. Demand for bandwidth is driving the expansion of optical transmission systems into homes and businesses of all size. Single wavelength fiber optic systems can support substantial data rates. However, services such as HDTV, on-demand TV programming, internet telephony, and telepresence can require a very high bandwidth.
Most current optical communication systems utilize digital transmissions of binary signals represented by 1-bits and 0-bits. Most state-of-the-art optical communications systems use multi-wavelength optical signals to achieve the desired bandwidth. Wavelength division multiplexing (WDM) is used to simultaneously transmit many high capacity optical signals over a single optical fiber. Each optical signal propagating in the WDM optical communications system occupies its own wavelength within the gain spectrum of the optical amplifiers that are used to offset the insertion loss of the optical cable and other optical network elements used to transmit the optical signal.
The increasing need for high bit-rate data transmissions through WDM optical communications system presents significant challenges to the fiber-optic telecommunications industry. One of these challenges is that optical communications systems experience a large power fluctuation when the optical path of one or more optical channel is switched to a different optical path. This is a fundamental limitation of the optical amplifiers used in the system. These amplifiers use optical power monitors to feedback signals to the amplifier control circuit that, in turn, adjusts the output power in order to maintain a constant gain for each of the WDM signals that are transmitted. The time that it takes the optical amplifier to re-adjust the power is a significant time, typically on the order of one mill-second. During this time, a significant degradation in the performance of the optical link is expected.